1. Field of the Invention
The present invention relates to a radio communication apparatus that operates with a battery and is connectable to multiple radio communication networks, and also to a radio communication method used in the radio communication apparatus.
2. Description of the Related Art
In recent years, along with advancement of radio communication technologies, radio communication apparatuses connectable to multiple radio communication networks employing different communication schemes have been proposed. Such a radio communication apparatus (for example, mobile communication terminal) connectable to multiple radio communication networks generally operates with a battery, and includes multiple network connection units (for example, connection units for a cellular phone network and for a wireless LAN) corresponding to the number of the connectable radio communication networks. In addition, each network connection unit generally has a power amplifier for amplifying a radio signal.
When the radio communication apparatus executes a handover from a currently-connected radio communication network to another radio communication network, the radio communication apparatus simultaneously activates both of a power amplifier of a network connection unit used for transmission and reception of a radio signal to and from the currently-connected radio communication network, that is, a radio communication network of a handover source, and a power amplifier of a network connection unit used for transmission and reception of a radio signal to and form a radio communication network of a handover destination. Accordingly, the radio communication apparatus can execute a so-called soft handover that is a handover executed with disconnection time of on-going communication being minimized.
However, the conventional radio communication apparatus mentioned above has the following problem. Specifically, when the radio communication apparatus executes the soft handover, is the radio communication apparatus simultaneously activates both of the power amplifier used for transmission and reception of the radio signal to and from the radio communication network of the handover source, and the power amplifier used for transmission and reception of the radio signal to and from the radio communication network of the handover destination. Therefore, an output voltage of the battery that is driving the power amplifiers drops.
Specifically, assume a case where the battery is used for more than a certain period of time after being charged, and then multiple power amplifiers are driven with the battery having its output voltage already dropped to a level lower than the output voltage of the battery fully charged. In this case, the output voltage may drop to a level which causes a protection circuit to operate. When the output voltage drops to the level which causes a protection circuit to operate, the on-going communication is disconnected.